Innate immune recognition of the single stranded RNA (ssRNA) virus and induction of a strong antiviral immunity play a critical role in the outcome of HCV infection. Alcohol consumption contributes to inflammation, innate immune defects, and HCV-induced progression of liver disease. Toll like receptor 7 and 8 recognizing ssRNA expressed in innate immune cells such as monocytes and dendritic cells (DC), have recently been novel targets in HCV therapy; however, little is known about the role of TLR7/8 in the pathomechanism of HCV infection. Our studies demonstrated that chronic HCV infection as well as alcohol treatment results in increased monocyte pro-inflammatory activation but impaired IFN? production by plasmacytoid dendritic cells. Therefore, we hypothesize that HCV interferes with antiviral host defense at the level of viral recognition receptors and by subverting pivotal functions of monocytes and dendritic cells. We propose that by modulating TLR7/8 activation in innate immune cells, HCV activates inflammatory pathways and alters IFN induction. We further postulate that alcohol exposure of innate immune cells alters TLR7/8-induced signaling. We hypothesize that TLR7/8-mediated signals play a role in HCV-induced alterations in myeloid dendritic cells and contribute to the reduced T cell responses in HCV infection by induction of CD4+CD25+ regulatory T cells. We further propose that alcohol amplifies defects in innate immune responses of HCV infected patients by interfering not only with TLR7/8 signaling but also with dendritic cell-induced T cell activation. The Specific Aims of this proposal are: 1. To determine the effect of alcohol exposure on TLR8-mediated signals in inflammatory activation in monocytes and macrophages in HCV infection by investigating the expression of TLR8 and the effect of TLR8 activation on MyD88-dependent signaling and Type I IFN-induction pathways and the effects of uptake of HCV-infected hepatoma cells in monocytes from HCV infected patients. 2. To investigate mechanisms by which alcohol modulates myeloid dendritic cell-mediated defects of T cell activation in chronic HCV infection by evaluating the effect of TLR8 activation and uptake of HCV-infected hepatoma cells on monocyte-derived DCs (mDC).differentiation, maturation, and T cell activating capacity. 3. To evaluate the effect of alcohol on IFN-lambda in HCV infection by testing dendritic-cell-mediated induction of regulatory T cells. 4. To assess the effect of alcohol on the role of TLR7 in plasmacytoid dendritic cells of HCV infected patients. Results from these experiments will provide novel information about the effects of alcohol on antiviral immunity and its role in the pathomechanisms of chronic HCV infection. PUBLIC HEALTH RELEVANCE: Hepatitis C virus (HCV) results in chronic liver inflammation which leads to chronic liver disease. Alcohol consumption worsens HCV liver disease. The common target of both HCV and alcohol use is the immune system where both HCV and alcohol use result in activation of inflammatory cells and inhibition of antigen- specific immune cell functions. The goal of this application is to identify specific mechanisms by which HCV and alcohol induce these abnormalities in innate immune cells by using specimens from patients with chronic HCV infection and in vitro methods to study the effects of alcohol.